To investigate the correlation between the serum levels of ischaemia-modified albumin (IMA) and disease severity in rats with acute pancreatitis (AP). A rat AP model was established and blood samples from each group were analysed at different time points. After the experiment, the pancreatic tissues of the rats were collected for pathological examination and the measurement of protein levels of NF-κB and NF-κB p65. Serum levels of amylase (α-AMY), tumour necrosis factor-α (TNF-α), interleukin (IL)-6 and IL-8 were also compared between groups of rats. The serum IMA concentration in the severe acute pancreatitis (SAP) group was greater than that in the mild acute pancreatitis (MAP) group. The levels of the NF-κB and NF-κB p65 proteins were increased in the MAP and SAP groups in a time-dependent manner. α-AMY, TNF-α and IL-6 were increased at all time points in the MAP and SAP groups. The increases were greatest at 24 h in the SAP group. In terms of pathological changes in the pancreas, renal and lung tissues, the damage in the SAP group was more obvious than that in the MAP group. Serum IMA level was associated with inflammatory markers and NF-κB p65 in rats with AP.